Flexible solid electrolyte for use in solid state cells and solid state cell including said flexible solid electrolyte

ABSTRACT

A solid state cell is provided including a sheet of flexible solid  electrte less than 0.1 mm in thickness between two electrodes wherein the flexible solid electrolyte is obtained from a mixture of about 80 to 95 weight percent solid electrolyte with about 5 to 20 weight percent of powdered Teflon.

GOVERNMENT INTEREST

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

FIELD OF INVENTION

This invention relates in general to the art of solid state cells, andin particular to a method of making a flexible solid electrolyte for usein solid state cells, to a flexible solid electrolyte so made, and to asolid state cell including said flexible solid electrolyte.

BACKGROUND OF THE INVENTION

Many solid state electrolytes used in solid state cells have usedionically conductive ceramics, glasses, and crystalline salts that areinherently brittle and thereby difficult to manufacture into thinstructures. The most common method used to prepare these materials aselectrolytes for solid state cells has been through pressed powderpelletization that may include sintering or fusing of the pellets atelevated temperatures. The pelletization process however, has not beensuitable for preparing thin electrolyte structures (<0.5mm thick) thatare needed for higher power solid state cell designs. This issignificant since a high power solid state cell would provide power forapplications in robotics, electric vehicle propulsion, weapon systemsand communications.

SUMMARY OF THE INVENTION

The general object of this invention is to provide a method of making aflexible, ionically conductive solid electrolyte for use in solid statebatteries. A more particular object of the invention is to provide amethod of preparing a flexible lithium tetrachloroaluminate (LiAlCl₄)electrolyte for use in solid state cells. A still further object of theinvention is to provide a method of making a flexible LiAlCl:electrolyte that is less fragile, and capable of being prepared thinnerthan press powder pelletization processes, thereby allowing thepreparation of higher power solid state cells.

It has now been found that the aforementioned objects can be attainedand a flexible solid electrolyte provided by a method of preparationcontaining Teflon powder as a mechanical binder that is roll milled withthe solid electrolyte component.

More particularly, according to the invention, a flexible solidelectrolyte is prepared by the steps of

(A) mixing about 80 to about 95 weight percent of powdered LiAlCl₄ withabout 5 to 20 weight percent of Teflon powder,

(B) ball or roll milling the dry mixture until the Teflon particlesthoroughly bind the electrolyte powder into a stiff coherent dough,

(C) roll or static pressing the milled mixture to a thickness of about 1mm and

(D) forming a cell sandwich by placing the rolled electrolyte mixturebetween an anode and a cathode and further reducing the cell thicknessto where the electrolyte layer is less than 0.1 mm thick. This step willalso form a cohesive bond between the solid electrolyte layer and theelectrode surfaces.

The solid electrolyte prepared according to this method is found to beflexible, freestanding, cohesively bonded to the electrode surfaces, andcapable of being used in solid state cells at elevated temperatureswithout physical degradation. In this connection, lithium intercalatinganode and cathode materials are used in the system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A flexible solid LiAlCl₄ electrolyte preparation utilizing 90 weightpercent LiAlCl₄ (-400 mesh powder, Anderson Physics grade) and, 10weight percent Teflon as the binder is roll milled into a coherent stiffdough and roll pressed into 1 mm thick freestanding flexible sheets. TheTeflon powder is obtained by precipitation from Dupont Teflon-60 aqueousemulsion using acetone. The precipitated Teflon is vacuum filtered andwashed with acetone followed by vacuum drying at 100° C. for 24 hours.The following steps are performed in an argon filled glove box to avoidmoisture contamination of the solid electrolyte. The solid electrolyte(LiAlCl₄) is ground to a fine mesh size (-400 mesh). A mixture of 90weight percent ground LiAlCl₄ and 10 weight percent dried Teflon ismechanically milled until a stiff coherent dough is obtained. The doughis then placed between two plastic sheets and roll pressed to athickness of about 1 mm. Two thin film electrodes (anode and cathode)that are prepared onto metal foils are placed on either side of therolled electrolyte sheet. The stacked cell components are then placed inbetween 2 plastic sheets and further roll pressed until the electrolytelayer thickness is reduced to less than 0.1 mm. The cell fabricatedusing the aforementioned method produces a solid state cell that has aflexible, cohesive, and freestanding characteristic that could not beobtained previously with electrolyte prepared using press powderpelletization.

The solid electrolyte in the invention can be any ionically conductiveelectrolyte material or mixture thereof. These include ionicallyconductive compounds generally referred to as "Lisicon" or inorganicceramic materials that are lithium ion conducting. A preferred "Lisicon"compound is Li₁₄ ZnGe₄ O₁₆. The ionically conductive materials alsoinclude compounds generally referred to as "Nasicon" or inorganicceramic materials that are sodium ion conducting. Preferred "Nasicon"compounds are Na.sub.(1+x) Zr₂ Si_(x) P.sub.(3-x) O₁₂ and Na₃ Zr₂ Si₂PO₁₂. The ionically conductive compounds can also be beta aluminas.These include materials such as Na₁.2 Al₁₁ O₁₇.1, Na_(1-x) NiAl₁₁O_(17+x/2), Na₁.67 MgAl₁₀.33 O₁₇, Na_(1-x) Ni Al_(11-x) O₁₇, andNa_(1-x) Zr₁ Al_(11-x) O₁₇. The solid electrolyte may also be of theionically conductive compound alkali tetrahaloaluminates having thegeneral formula XAlY₄ where X may be Li, Na, K, Rb or Cs, and Y may beCl, Br, I, or F. Preferred among these compounds is LiAlCl₄.

We wish it to be understood that we do not desire to be limited to theexact details of construction as described for obvious modificationswill occur to a person skilled in the art.

What is claimed is:
 1. A flexible solid electrolyte for use in solidstate cells, said flexible solid electrolyte comprising a milled mixtureof about 80 to 95 weight percent solid electrolyte with about 5 to 20weight percent of powdered Teflon and wherein the solid electrolyte isof the ionically conductive compounds alkali tetrahaloaluminates havingthe general formula XAlY₄ where X is a metallic element selected fromthe group consisting of Li, Na, K, Rb and Cs, and where Y is a halogenselected from the group consisting of Cl, Br, I and F.
 2. A flexiblesolid electrolyte for use in solid state cells, said flexible solidelectrolyte comprising a milled mixture of about 80 to 95 weight percentsolid electrolyte with about 5 to 20 weight percent of powdered Teflonand wherein the solid electrolyte is LiAlCl₄.
 3. A flexible solidelectrolyte for use in solid state cells, said flexible solidelectrolyte comprising a milled mixture of about 90 weight percentLiAlCl₄ with about 10 weight percent of powdered Teflon.
 4. A flexiblesolid electrolyte for use in solid state cells, said flexible solidelectrolyte comprising a milled mixture of about 80 to 95 weight percentsolid electrolyte with about 5 to 20 weight percent of powdered Teflonand wherein the solid electrolyte is of the ionically conductivecompounds that are inorganic ceramic materials that are lithium ionconducting and referred to as Lisicon.
 5. A flexible solid electrolytefor use in solid state cells, said flexible solid electrolyte comprisinga milled mixture of about 80 to 95 weight percent solid electrolyte withabout 5 to 20 weight percent of powdered Teflon and wherein the solidelectrolyte is Li₁₄ Zr₁ Ge₄ O₁₆.
 6. A flexible solid electrolyte for usein solid state cells, said flexible solid electrolyte comprising amilled mixture of about 80 to 95 weight percent solid electrolyte withabout 5 to 20 weight percent of powdered Teflon ad wherein the solidelectrolyte is of the ionically conductive compounds that are inorganicceramic materials that are sodium ion conducting and referred to asNasicon.
 7. A flexible solid electrolyte for use in solid state cells,said flexible solid electrolyte comprising a milled mixture of about 80to 95 weight percent solid electrolyte with about 5 to 20 weight percentof powdered Teflon, and wherein the solid electrolyte is selected fromthe group consisting of Na.sub.(1+x)Zr₂ Si_(x) P.sub.(3-x) O₁₂ and Na₃Zr₂ Si₂ PO₁₂.
 8. A flexible solid electrolyte for use in solid statecells, said flexible solid electrolyte comprising a milled mixture ofabout 80 to 95 weight percent solid electrolyte with about 5 to 20weight percent of powdered Teflon, and wherein the solid electrolyte isNa.sub.(1+x) Zr₂ Si_(x) P.sub.(3-x) O₁₂.
 9. A flexible solid electrolytefor use in solid state cells, said flexible solid electrolyte comprisinga milled mixture of about 80 to 95 weight percent solid electrolyte withabout 5 to 20 weight percent of powdered Teflon, and wherein the solidelectrolyte is Na₃ Zr_(z) Si₂ PO₁₂.
 10. A flexible solid electrolyte foruse in solid state cells, said flexible solid electrolyte comprising amilled mixture of about 80 to 95 weight percent solid electrolyte withabout 5 to 20 weight percent of powdered Teflon, and wherein the solidelectrolyte is of the ionically conductive compounds referred to as betaalumina.
 11. A flexible solid electrolyte for use in solid state cells,said flexible solid electrolyte comprising a milled mixture of about 80to 95 weight percent solid electrolyte with about 5 to 20 weight percentof powdered Teflon, and wherein the solid electrolyte is selected fromthe group consisting of Na₁.2 Al₁₁ O₁₇.1, Na_(1+x) NiAl₁₁ O_(17+x/2),Na₁.67 MgAl₁₀.33 O₁₇, Na_(1+x) MgAl_(11-x) O₁₇, Na_(1+x) NiAl_(11-x)O₁₇, and Na_(1+x) Zr₁ Al_(11-x) O₁₇.
 12. A flexible solid electrolytefor use in solid state cells, said flexible solid electrolyte comprisinga milled mixture of about 80 to 95 weight percent solid electrolyte withabout 5 to 20 weight percent of powdered Teflon, and wherein the solidelectrolyte is Na₁.2 Al₁₁ O₁₇.1.
 13. A flexible solid electrolyte foruse in solid state cells, said flexible solid electrolyte comprising amilled mixture of about 80 to 95 weight percent solid electrolyte withabout 5 to 20 weight percent of powdered Teflon, and wherein the solidelectrolyte is Na_(1+x) NiAl₁₁ O_(17+x/2).
 14. A flexible solidelectrolyte for use in solid state cell, said flexible solid electrolytecomprising a milled mixture of about 80 to 95 weight percent solidelectrolyte with about 5 to a 20 weight percent of powdered Teflon, andwherein the solid electrolyte is Na₁.67 NgAl₁₀.33 O₁₇.
 15. A flexiblesolid electrolyte for use in solid state cells, said flexible solidelectrolyte comprising a milled mixture of about 80 to 95 weight percentsolid electrolyte with about 5 to 20 weight percent of powdered Teflon,and wherein the solid electrolyte is Na_(1+x) MgAl_(11-x) O₁₇.
 16. Aflexible solid electrolyte comprising a milled mixture of about 80 to 95weight percent solid electrolyte with about 5 to 20 weight percent ofpowdered Teflon, and wherein the solid electrolyte is Na_(1-x)NiAl_(11-x) O₁₇.
 17. A flexible solid electrolyte comprising a milledmixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 weight percent of powdered Teflon, and wherein the solidelectrolyte is Na_(1+x) Ar₁ Al_(11-x) O₁₇.
 18. A flexible solidelectrolyte comprising a milled mixture of about 80 to 95 weight percentsolid electrolyte with about 5 to 20 weight percent of powdered Teflon,and wherein the solid electrolyte is LiN.
 19. A solid state cellincluding a sheet of flexible solid electrolyte less than 0.1 mm inthickness between two electrodes wherein the flexible solid electrolyteis obtained from a mixture of about 80 to 95 weight percent solidelectrolyte with about 5 to 20 percent of powdered Teflon, and whereinthe solid electrolyte is of the ionically conductive compounds alkalitetrahaloaluminate having the general formula XAlY₄ where X is ametallic element selected from the group consisting of Li, Na, K, Rb andCs, and where Y is a halogen selected from the group consisting of Cl,Br, I and F.
 20. A solid state cell according to claim 19 wherein thealkali tetrahaloaluminate is LiAlCl₄.
 21. A solid state cell including asheet of flexible solid electrolyte less than 0.1 mm in thicknessbetween two electrodes wherein the flexible solid electrolyte isobtained from a mixture of about 80 to 95 weight percent solidelectrolyte with about 5 to 20 percent of powdered Teflon, and whereinabout 90 weight percent of LiAlCl₄ is mixed with about 10 weight percentof Teflon.
 22. A solid state cell including a sheet of flexible solidelectrolyte less than 0.1 mm in thickness between two electrodes whereinthe flexible solid electrolyte is obtained from a mixture of about 80 to95 weight percent solid electrolyte with about 5 to 20 percent ofpowdered Teflon, and wherein the solid electrolyte is of the ionicallyconductive compounds that are inorganic ceramic materials that arelithium ion conducting and generally referred to as Lisicon.
 23. A solidstate cell including a sheet of flexible solid electrolyte less than 0.1mm in thickness between two electrodes wherein the flexible solidelectrolyte is obtained from a mixture of about 80 to 95 weight percentsolid electrolyte with about 5 to 20 percent of powdered Teflon, andwherein the Lisicon compound is Li₁₄ Zr₁ Ge₄ O₁₆.
 24. A solid state cellincluding a sheet of flexible solid electrolyte less than 0.1 mm inthickness between two electrodes wherein the flexible solid electrolyteis obtained from a mixture of about 80 to 95 weight percent solidelectrolyte with about 5 to 20 percent of powdered Teflon, and whereinthe solid electrolyte is of the ionically conductive compounds that areinorganic materials that are sodium ion conducting and referred to asNasicon.
 25. A solid state cell including a sheet of flexible solidelectrolyte less than 0.1 mm in thickness between two electrodes whereinthe flexible solid electrolyte is obtained from a mixture of about 80 to95 weight percent solid electrolyte with about 5 to 20 percent ofpowdered Teflon, and wherein the solid electrolyte is selected from thegroup consisting of Na.sub.(1+x) Zr₂ Si_(x) P.sub.(3-x) O₁₂ and Na₃ Zr₂Si₂ PO₁₂.
 26. A solid state cell including a sheet of flexible solidelectrolyte less than 0.1 mm in thickness between two electrodes whereinthe flexible solid electrolyte is obtained from a mixture of about 80 to95 weight percent solid electrolyte with about 5 to 20 percent ofpowdered Teflon, and wherein the solid electrolyte is Na.sub.(1+x) Zr₂Si_(x) P.sub.(3-x) O₁₂.
 27. A solid state cell including a sheet offlexible solid electrolyte less than 0.1 mm in thickness between twoelectrodes wherein the flexible solid electrolyte is obtained from amixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 percent of powdered Teflon, and wherein the solid electrolyte isNa₃ Zr₂ Si₂ PO₁₂.
 28. A solid state cell including a sheet of flexiblesolid electrolyte less than 0.1 mm in thickness between two electrodeswherein the flexible solid electrolyte is obtained from a mixture ofabout 80 to 95 weight percent solid electrolyte with about 5 to 20percent of powdered Teflon, and wherein the solid electrolyte is of theionically conductive compounds generally referred to as beta alumina.29. A solid state cell including a sheet of flexible solid electrolyteless than 0.1 mm in thickness between two electrodes wherein theflexible solid electrolyte is obtained from a mixture of about 80 to 95weight percent solid electrolyte with about 5 to 20 percent of powderedTeflon, and wherein the solid electrolyte is selected from the groupconsisting of Na₁.2 Al₁₁ O₁₇.1, Na_(1-x) NiAl₁₁ O_(17+x/2), Na₁.67MgAl₁₀.33 O₁₇, Na_(1+x) MgAl_(11-x) O₁₇, Na_(1+x) NiAl_(11-x) O₁₇, andNa_(1+x) Zr₁ Al_(11-x) O₁₇.
 30. A solid state cell including a sheet offlexible solid electrolyte less than 0.1 mm in thickness between twoelectrodes wherein the flexible solid electrolyte is obtained from amixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 percent of powdered Teflon, and wherein the solid electrolyte isNa₁.2 Al₁₁ O₁₇.1.
 31. A solid state cell including a sheet of flexiblesolid electrolyte less than 0..1 mm in thickness between two electrodeswherein the flexible solid electrolyte is obtained from a mixture ofabout 80 to 95 weight percent solid electrolyte with about 5 to 20percent of powdered Teflon, and wherein the solid electrolyte isNa_(1+x) NiAl₁₁ O_(17+x/2).
 32. A solid state cell including a sheet offlexible solid electrolyte less than 0.1 mm in thickness between twoelectrodes wherein the flexible solid electrolyte is obtained from amixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 percent of powdered Teflon, and wherein the solid electrolyte isNa₁.67 MgAl₁₀.33 ₁₇.
 33. A solid state cell including a sheet offlexible solid electrolyte less than 0.1 mm in thickness between twoelectrodes wherein the flexible solid electrolyte is obtained from amixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 percent of powdered Teflon, and wherein the solid electrolyte isNa_(1+x) MgAl_(11-x) O₁₇.
 34. A solid state cell including a sheet offlexible solid electrolyte less than 0.1 mm in thickness between twoelectrodes wherein the flexible solid electrolyte is obtained from amixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 percent of powdered Teflon, and wherein the solid electrolyte isNa_(1-x) NiAl_(11-x) O₁₇.
 35. A solid state cell including a sheet offlexible solid electrolyte less than 0.1 mm in thickness between twoelectrodes wherein the flexible solid electrolyte is obtained from amixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 percent of powdered Teflon, and wherein the solid electrolyte isNa_(1-x) Zr₁ Al_(11-x) O₁₇.
 36. A solid state cell including a sheet offlexible solid electrolyte less than 0.1 mm in thickness between twoelectrodes wherein the flexible solid electrolyte is obtained from amixture of about 80 to 95 weight percent solid electrolyte with about 5to 20 percent of powdered Teflon, and wherein the solid electrolyte isLiN.